Inkjet printing propels droplets of ink onto media to create a digital image. Thermal ink jet (TIJ) printing uses print cartridges that contain a series of firing chambers, each containing a resistive heater in a flow channel filled with ink. The firing chambers are often constructed by photolithography. In order to eject a droplet from each firing chamber, a pulse of current is passed through the heating element, causing rapid vaporization of a thin film immediately above the resistor to form a bubble. The rapid expansion of the bubble propels the remaining ink in the chamber through an orifice, ejecting a droplet of ink onto the media. Collapse of the vapor bubble pulls ink back into the firing chamber through a narrow channel attached to an ink reservoir, refilling the firing chamber for another droplet ejection.